Pulse communication system



Aug. 12, 1947.

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Ziff/wave Jmr/aa/ C. W. HANSELL PULSE COMMUNICATION SYSTEM Filed Sept. 16, 1943 Tllzl.

4 Sheets-Sheet 1 INVENTOR ATTORNEY Aug. 12, 1947.

c. w. HANsELL PULSE COMMUNICATION SYSTEM Filed sept. 1e; 194s 4 Sheets-Sheet 2 mvENToR )m/ffu.

ATTORNEY All@ 12 1947' c. w. HANsELL PULSE COMMUNICATION SYSTEM 4 Sheets-Sheet 3 Filed Sept.. 16, 1943 (Nic- INVENTOR a' WMA/faz.

ATTORNEY Aug. 12, 1947. C, w, HANSELL 2,425,314I

PULSE COMMUNICATION SYSTEM Patented ug. 12, 1947 CATION SYS Clarence W. Hanaell. hloint, N. Y., e

to Radio Corporation of America, a corporation of Delaware Application September 16, i943, Serial No. il2,585

(Cl. Z50-6) The present invention relates to a communication system in which means is provided to limit and select the range of distances over which communication is carried out and to exclude undesired communications or interference from stations at other distances.

More specifically, the invention provides a distance selective pulse communication system in which the range of distances within which communication is possible is controllable, so that any pair of stations at a particular distance from one anothermay be used for communication in a manner which excludes interference from stations at other distances. `By means of this distance selective feature, which may be used, if desired, in combination with great angular selectivity due to antenna directivity patterns, as well as a certain amount of frequency selectivity, and threshholding and limiting in the receiver, there is provided a degree of freedom from interference and jamming which would be difficult if not impossible to obtain by other systems.

In the practice of the invention, communication is carried on by means of pulses of energy whose length in time is very short compared with the time interval between pulses, and which pulses are repeated at a pulse rate or frequency which is higher than the highest modulation frequencies of the signals to be transmitted. Because of the fact that transmission or reception utilizes only a small percentage of the total time, I am able. among other things, to accomplish two-way or duplex transmission and reception between a pair of stations without interference from the trans. mitter into the receiver at the same station. This is done by arranging the transmission and reception time periods at any one station so that they are different and do not coincide in time. Thus, during periods of pulse transmission from a station, reception at theY same transmitting station is suppressed and output from the receiver at this same station is unaffected by its own transmitter. The waves of each transmitting station are received at the other station on a receiver which is made responsive substantially only to pulses being received at a particular controllable pulse rate. Also, the receiver at each station is controlled to make it responsive only to received signal pulses distinct from its own transmitted pulses. It is desirable in the practice of the invention that transmission and reception be carried out on the same or nearly the same radio carrier frequencies.

In the system of the present invention, it is intended that when the transmitter at, say. station l transmits a pulse, this pulse is received at station 2. utilized for reproducing modulations, and also utilized for controlling the timing of pulses transmitted from station 2. Pulses received from station 2 at station l, in turn are utilized to control the timing of pulses from station l. Thus, a sort of closed pulsing circuit or round robin situation is set up in which the time rate of pulses at both stations is locked together so that the transmitters of the two stations transmit or re pulses alternately and at equal pulsing rates. In the receiver of each station, there are provided adjustable time delay regeneration, or receiver sensitivity keying or modulation circuits responsive to received pulses which cut oi the receivers during time periods when pulses are not due to be received from the corresponding stations but which cause the receiver to be in a condition to respond to desired pulses from the corresponding stations. By this means, any one transmitting and receiving station can be made responsive only to other stations'at a particular distance or narrow range of distances according to the adjustment of the keying circuit time delay in each receiver and the more or less fixed pulse time delay present in the circuits between receiver input and transmitter output. With the system of the invention, any other pulsing transmitter at some other distance would automatically require a different pulsing rate than that for which the receiver of a particular station is adjusted and consequently no response to transmitters at undesired distances would be obtained. Therefore, the operator at any one station may, at will, adjust his equipment to be responsive only to another station at a desired distance. In addition, by means of sharp directivity, the operator at any one station may limit operation to another station in only. one narrow range of directions. It is therefore possible, according to the invention, for any one station to limit operations to a particular small area at a selected distance and direction, so that jamming from other similar types of pulsing communication equipment can be greatly reduced, or Virtually eliminated.

In order to achieve a selected narrow range of distances within a larger range of selectable distances over which communication may be carried out, in accordance with the present invention, it is important that the pulse periods be very short with relatively long time periods between pulses. I prefer to employ short pulses of the order of one microsecond and less. The distance selectively obtainable by the invention is inversely proportional to the pulse time period. The minimum distance for which the system may be adjusted is also inversely proportional to the pulse time period. The shorter the pulse, the smaller the range of distances within a larger selectable range to which the system may be adjusted to be selective. Thus, the systemv of the invention may be selectable, or adjustable, for use over a range of distances between approximately one-quarter of a mile and several miles extending up to fifty miles, for example. By adjusting the length of the pulse, it is possible to select for communication an extremely small range of distances within this larger range, in order to eliminate interference from stations outside this small selected range. If, for example, the time interval of the pulse is one microsecond, then it is possible to differentiate between stations over a wide range of distances which diifer in distance with respect to some other station by as little as 300 meters'. In practice, considering the present state of development, it is possible to produce pulses as short as one-tenth of a microsecond.

The pulse repetition rate or frequency must be higher than the highest modulation frequency required in any particular system of communication to which the invention is to be applied. For example, in a single channel voice communication system requiring modulation frequencies up to 3000 cycles per second, it is desirable to use a pulse repetition rate of not less than 9000 cycles per second, although pulse rates as low as 5000 cycles per second will give intelligible communication.

In some cases the modulation may require the pulse repetition rate to be so high that there is insuiiicient time between pulses to accommodate travel of the waves out to a distant station and back. In such cases it is still possible to operate by letting two or more pulses exist in the space circuit simultaneously although, of course, in this instance there will be more than one distance at which communication is possible. In fact, theoretically, there are always a series of discrete distances at which one set of adjustments will provide communication, though, in practice, this will not be very troublesome.

Although the invention is hereafter described with particular reference to a system employing radio communication at ultra high frequencies, it should be understood that the principles are also applicable to wire line communication, submarine signalling or to any other kind of communication by means of traveling waves.

A more detailed description of the invention follows in conjunction with a drawing, wherein:

Fig, 1 diagrammatically illustrates, in box form, a pair of radio stations equipped in accordance with the present invention for duplex communication by means of very short pulses of extremely high frequency energy;

Fig. 2 is a schematic circuit diagram showing in detail the pulse receiver and pulse demodulator circuits which can be used in the stations of Fig. 1;

Figs. 3 and 4 illustrate alternative forms of pulse demodulator and audio amplifier circuits which can be used in the stations of Fig. 1; and

Figs. 5 and 6 illustrate two different forms of adjustable pulse delayer and modulator circuits and pulse transmitters, which can be used in the stations of Fig. 1.

Referring to Fig. 1, there is shown a, distance selective radio communication system comprising a pair of radio stations I and 2 for effecting twoway communication with each other. In view of the fact that both stations are similarly equipped and the apparatus identically labeled in the drawing. only one of these stations will be described. Both stations are pulse repeater stations for repeating short pulses extremely high frequency energy back and forth between them. Pulses of high frequency energy leaving station I travel to station 2 from which they are repeated back to station I, then again repeated to station 2, etc. As a result, each station transmits a succession of pulses repeated at a frequency determined by the time required for waves to passv over the space circuit plus time delays in the equipment. Thus, by providing at both repeater stations means for modulating the time delay of pulses passing through the equipment, there is caused *to occur at both repeater stations a corresponding response in pulse rate or frequency. The variations in pulse rate or frequency at the station receiving the modulated pulses are demodulated, as a result of which it is possible to carry on communication in either direction.

Each of the stations I and 2 of Fig. l includes a pulse transmitter I2 feeding a transmit-receive device 9 to be described in more detail hereafter, the latter in turn being associated with a suitable directive antenna I3, here shown by way of example only as a parabolic reflector having a radiator at its focus. The transmit-receive device 9 is also coupled to apparatus II comprising a pulse receiver with a pulse rate selective gating circuit. A portion of the output of apparatus I I is fed into an adjustable pulse delayer and modulator circuit I0, which includes a pulse oscillator, the circuit I0 in turn being coupled to the pulse transmitter I2 for controlling the same. Another portion of the output from apparatus II is fed via lead I4 to a pulse demodulator and audio amplifier circuit I5 from which the demodulated energy is fed to a balancing network I6. Associated with the network I6 is a telephone station I8, including the usual transmitting and receiving equipment. The telephone station I8 at each repeater station includes an earphone and a microphone, like any well known telephone station. A connection also extends from the unit I6 vial lead I9 to the adjustable I pulse delayer and modulator circuit I0.

The antenna I3 is employed both to radiate the high frequency pulses and to receive pulses from the remote station. The radiator at the focus of the parabolic reector is coupled over a transmission line 8 to the transmit-receive device 9, the purpose of which is to uncouple the receiver from the transmission line system 8 While the transmitter is operating and to uncouple the transmitter from the transmission line system 8 when it is not operating, so that between transmitted pulses maximum received power from the antenna may be delivered to the receiver. The transmit-receive device 9 may be any suitable circuit employed for this purpose, several of which have been developed for use with military radio locating pulsing systems. One suitable transmit-receive device which may be employed is described in copending application Serial No, 477,435, filed February 27, 1943, by N. E. Lindenblad. Another suitable transmit-receive device is described in copending application Serial No. 466,274, filed November 20, 1942, by E. I. Anderson. However, because of its superior performance, I prefer to use a type of transmit-receive device invented by N. E. Lindenblad which is described in copending application Serial No. 504,373, nled September 30, 1943.

The pulses received by the transmit-receive l device 9 are passed on to the pulse receiving unit II via lead 'I and a portion of the output from unit II is passed on to the adjustable pulse delayer and modulatorunit I0, in order to control the exact timing of the pulsing of transmitter I2. .is mentioned before, a portion of the pulse output of the receiver I I is also passed by way of lead I4 to the pulse demodulator and audio amplier unit I5, the output of which in turn is fed to the balancing network I6. Network I6 comprises suitable hybrid coils of the type well known in the telephone art, for preventing interference between transmitting and receiving energy. By means of the use of balancing network I6, demodulated energy from unit I can only go to the earphone or utilization circuit of telephone station I8 and cannot reach lead' I9 or be carried to unit I0. Likewise, by virtue of the network I6, energy from the microphone of telephone station I8 can only go to unit Ill over lead i9, and cannot go to unit I5. It will thus 1 be seen that the primary function of the network I6 is to prevent energy from unit I5 from reaching unit I0 over lead I9 in sumcient volume to cause singing, a condition sometimes found in telephone practice.

The circuit apparatus of units Il and I5 are shown in detail in Fig. 2, to be described later. Alternative forms" of apparatusfor unit l5 are shown in detail in Figs. 3 and 4, also to be described later.

The circuit apparatus for units I0 and i2 are shown in detail in Figs. 6 and 7, to be described later.

A general description of the operation of the system of Fig. 1 will now be given. Each transmitter I2 at the two stations sends out pulses which are initiated by 'a pulse oscillator associated with and contained within the adjustable pulse delayer and modulator I0. By arranging the directive antennas I3, I3 at both stations so that they are pointed toward each other, each station will receive the pulses from the other station. At each station, the receiver unit Il is of a type which provides synchronous gating to receive .pulses when the pulse repetition rate is correct.

The term gating is here employed to mean controlling the receiving apparatus ,so as to renderv the receiver responsive at such times when p ulses' are due to arrive. If, for example,V eachtransgate themselvesto admit only one chain of pulses repeated at'a rate of 20,000 pulses per second, plus or minus the amount of pulse frequency change which may be required by signal modulations. The required range of pulse rate or frequency is obtained by making the receiver responsive periods somewhat longer than the length of the transmitted pulses. In order to make the system distance selective, pulses from the output of the receiver apparatus II at each station are given an adjustable time delay in unit I0`and then utilized to control the time of pulsing of the transmitter I2. This may be done by using the received. pulse to synchronize the operation of the pulse oscillator in unit IIJ which controls the pulsing of the transmitter I2. Once this synchronism has been accomplished at both stations, by suitable adjustment of the time delays, then We have a distance selective communication system.

It is preferred, in operating the system of Fig. 1, that the pulsing oscillator in unit I0 at each station be turned ofP during idle periods, thereby stopping transmission, but that the receivers be maintained operative, except for the self-synchronizing feature, during these idle periods. Then, when one station is to be used to call the other station, its time delay in unit I0 is set for minimum, corresponding to the maximum range of distance, its receiver gating synchronizing circuits are made operative, and its pulsing oscillator in unit I0 turned on" and the other station called by voice, tone signal or any other calling modulation. The attendant at the second station having heard the call, which happens when his gated receiver drifts through synchronism with the distant calling station, then switches in his locking circuits for holding his receiver gating in synchronism continuously tothe particular calling station. He then starts his transmitter pulsing oscillator in his unit I0 and adjusts the time delay of his system until he can hear his own speech coming back from the calling station, ar the receiver of the calling station locks in to the transmitter of the called station. Both stations are jthen in condition for two-way communication, and the attendant at the called station knows from the adjustment of his timedelay cir cuit what the exact distance is to the calling sta.- tion.

An alternative method of operation which can be used, particularly when there are a plurality of stations greater than two, similarly equipped in accordance with the invention, is for the operator of each of a number of unused stations to set his time delay circuit to a minimum corresponding to a maximum range of distance. Then, when any one station is to be used to call any other station, the operator at the calling station merely adjusts his time delay circuit to correspond with the distance to the station to be called. This adjustment should automatically lock the two stations together, so that the two-way communication can be carried on between them. This communication is protected from interference by the distance selectivity feature.

, pulses at any two stations in communication with each other ismodulated. It will thus be evident that the system of Fig. 1 is particularly useful in cases where it is desired to modulate the pulse rate or pulse frequency for effecting two-way communication between a pair of similarly equipped stations on extremely short pulses of ultra high frequency energy.

Fig. 2 shows in detail circuit arrangements for the apparatus of units Il and I5 of Fig. 1. The circuits of nits II and I5 in Fig. 2 are separately enclosed by dotted lines, and separately labeled.

Referring to Fig. 2 in more detail, the unit II comprising the pulse receiver with pulse rate selective gating" circuit comprises a high frequency pulse oscillator-detector 20 constituted by a pair of I frequency selective circuits A and B tuned to the frequency of the carrier wave, a pulse coupling tube ampliiier 2l whose input is coupled to the output of the oscillator-detector 20, and a signal pulse synchronized pulse oscillator 22, whose input is coupled to the output of the amplivice S of Fig. 1.

ner 2i. Output from the synchronized pulse oscillator 22 is taken by leads 28, which extends to the apparatus of unit I of Fig. 1 or to the apparatus of unit 40 of Fig. 6, to be later described. A portion of the output of the pulse oscillator 22 is also passed on by way of leads-29 to unit I5,

-which is shown in Fig. 2 as comprising a pair of vacuum tubes 23 and 24 constituting the pulse demodulator and modulation frequency amplifier. 'I'he tuned circuit A of the high frequency pulse oscillator-detector 20 is coupled by way of a transmission line 1 to the transmit-receive de- 'Ihe vacuum tube circuit 20 is normally in a non-conductive or current cut-off condition, by virtue of relatively large negative bias potential placed on the control grid of tube 20 over lead 25, due to grid rectification occurring in the synchronized signal pulse oscillator 22. Thus, the pulse oscillator-detector 20 is normally in a non-oscillating condition. Synchronized pulse oscillator 22, however, is a blocking oscillator type and oscillates continuously at a frequency slightly lower than the incoming signal pulse rate. At regular intervals, When oscillator 22 passes anode current (which occurs when condenser 26 discharges), the grid of tube 22 is made momentarily positive and simultaneously drives positive the grid of oscillator-detector tube 20 and pulse coupling tube amplifier 2|. This positive pulsing of the tube 20 causes oscillations to start in the tube circuit 20. This is because the tube 20 passes through a condition of zero high frequency resistance at the moment of transition from the oscillating to the non-oscillating condition, when its control electrode is pulsed positively, at which time it will begin oscillating and be extremely sensitive and responsive to the incoming pulses of radio frequency energy from line 1. Although the tube circuit 20 is extremely sensitive to received signal power, at or near this period of zero resistance, the oscillator-detector 20 is very insensitive and affected relatively little by received power before and after this period of zero resistance. The exact timing of oscillations of tube circuit 20 is controlled by the incoming energy *over line 1. Oscillator-detector tube 20 will oscillate until quenched by the negative bias from the pulse oscillator 22 which occurs immediately after condenser 26 discharges. After the discharge of condenser 26, the tube 20 is cut-off, leaving its grid highly negative. Thus, it can be said that the oscillator-detector tube circuit 20 is like a superregenerative detector which is sensitive to received signal energy only during the time period when it is passing through the condition of nearly zero alternating current resistance. As for the blocking oscillator 22, this can take either the form shown in my United States Patent No. 1,898,181, granted February 21, 1933, or the form shown in Tolson et al. Patent No. 2,101,520, granted December 7, 1937. In my patent supra, the controlling time constant circuit of the oscillator is in the anode circuit, while in the Tolson et al. patent the controlling time constant circuit is in the grid circuit. f

As soon as the oscillator-detector tube 20 begins oscillation under control of the incoming signal, it passes increasing anode current which causes a negative direct current pulse of potential to be delivered to the control grid of coupling tube amplifier 2|, this last tube in turn amplifying and reversing the polarity of the impressed pulse to thereby deliver a positive pulse to the control grid of oscillator 22, thus exerting an eiIect on the timing of the pulses of the oscillator tube circuit 22. In efiect, therefore, the oscillator tube circuit 22 opens the "gate or controls the periods of responsiveness of tube 20 in order to lallow signal pulses to go through the receiver unit yto thereby synchronize the oscillator 22. Pulse oscillator 22 has a natural pulse repetition rate of its own. which is approximately the same as the repetition rate of the input pulses and is therefore readily synchronized by the input pulses. The input pulses cause a small time delay in the cutting oil! of tube 22, which delay varies, as

necessary, to maintain synchronism. It will thus be evident that any small lack of synchronism of the oscillator 22 compared with the incoming pulse rate is automatically corrected by the received signal pulses. The entire system, once adjusted so that it is held in synchronism by received pulses, follows modulation of the frequency of the received pulses.

The output of constant amplitude pulses4 from the signal pulse synchronized pulse oscillator 22 of receiving unit II is impressed by way of leads 29 upon detector unit I5 which is the pulse demodulator and modulation frequency amplifier. Frequency modulations of the pulse rate are demodulated in detector unit I5. This unit I5 is shown as consisting of a pair of vacuum tubes 23 and 24 having a commonvcathode resistance 2l. The two tubes 2,3 and 24 are so arranged that for an average pulse rate applied to leads 29, both tubes 23 and 24 will carry equal currents. A variation of the pulse rate, however, impressed upon these tubes will cause a differential variation in the two tube currents which shows up as a push-pull variation of potential and current in output leads 30. The greater the current ow in common cathode resistor 21 due to an increased number of pulses applied to the grid of tube 23, over and above the average pulse rate, the more negative will be the bias on the grid of tube 24, as a result of which there will be less current in the output of tube 24. If fewer .pulses are applied to tube 23 than the average pulse rate, the current conditions of both tubes 23 and 24 will be reversed from that just described.

Interference from undesired stations is'discriminated against; first, because of the directivity of the antennas of the vstations in communication with each other; secondly, by virtue of the frequency selectivity of the radio frequency circuits including the effective selectivity of the circuits A and B of the vpulse oscillator-detector 20 asit passes through zero high frequency resistance, and thirdly, vby the pulse rate selectivity ofthe pulse oscillator 22. Oncev synchronism has been established. to a particular train of received pulses,

then timing selectivity will'auto'matically be util-4 ized because the pulsesv received between periods of nearly zero resistance in the pulse oscillatordetector circuit` 2l)l have substantially no effect upon the receiver of Fig. 2.

Figs. 3 and 4 show alternativeV vacuum tubes 'III and 1I and a double diode rectifier 12. The multi-vibrator circuit' 10, 1I is known in the art as'the Eccles-Jordan type, and lhas two 29 above a certain potential causes the multiuforms of pulsev demodulators which can be usedfor unit I5 -and versed. The rectifier 12, which is connected to` the anodes of the tubes and 1| of the multivibrator, passes current each time the vibrator flips or changes its condition of stability. Thus, the average current passed by the rectier is proportional to the number of flips or changes of stability of the vibrator; or, putting it in other words, to the number of incoming positive pulses applied to the vibrator, but this average current passed by the rectifier 12 is independent of the amplitude of these pulses over a range. Thus, the rectier current available in output circuit 13 is proportional to the pulse frequency but nearly independent of the pulse amplitude. If the input pulses are frequency modulated,- then the average current through the double diode rectifier 12 will be substantially proportional to the frequency or rate but substantially independent of the amplitude of the input pulses so long as the amplitude is above a threshold value. The arrangement of Fig. 3 thus acts as a thresholder, limiter and demodulator of 1requency modulated pulses. Inputs which are too weak will not change the stability condition of the multi-vibrator, while inputs greater than that needed to change the stability of the multi-vibrator have no increased effect over and above an input sufficient to change the condition of equilibrium of the multi-vibrator.

Fig. 4 is another form of thresholder, limiter and pulse demodulator for unit I5. 'I'he system of Fig. 4 includes an unbalanced flip-flop or multi-vibrator circuit (sometimes called a trigger circuit) having tubes 14 and 15 in combination with an audio amplier consisting of tubes 16 and 11. The unbalanced multi-vibrator circuit 14, has one degree of electrical stabilit and has a stable state and an active state. After input pulses throw the multi-vibrator circuit .to the active state or condition, the circuit automatically restores itself or throws itself back to the stable state after an interval of time about equal to half the time interval between pulses, when the pulses have an average repetition rate. It should be noted that the anode of tube 'I4 is connected to the grid of tube '|5 through condenser C, while the anode of tube 15 is connected to the grid of tube 'I4 through resistor R, thus providing diierent types of feed-back between the two tubes. The time for the circuit to throw its lbalance back is constant but the time between pulses is varied by the modulation. It will thus be seen that the percentage time occupied by the unbalanced flip-nop or multi-vibrator circuit in the stable state position or the other varies with the pulse rate, and this percentage unbalance one way or the other provides a pushpull modulation frequency output which passes through the resistance-capacity low pass filter 18 and is utilized by the audio amplifier 16, 11. Audio amplifier .tubes 16, 11 are both arranged to pass current at all times. In the system of Fig. 4, if the rate or frequency of the control pulses is modulated, the percentage time spent by the flip-flop circuit 14, 15 in one condition or the other will be modulated and this results in a differential variation of the average anode currents of the two tubes 14, 15. This differential variation provides the output potential at the modulation frequency, which is amplified in tubes 16 and 11.150 provide a final modulation audio frequency output in leads 19. The condenser 80 across the grids of the audio amplifier is a bypass condenser which more or less short-circuits energy of the pulse frequency.

Fig. 5 shows in detail the combined` units l0 and I2 of Fig.- 1. In Fig. 5, the adjustable pulse delayer and modulator comprises a pair of vacf uum tubes and 8|, arranged in the form of a flip-flop or unbalanced multi-vibrator circuit having one degree of electrical stability, similar to that shown in Fig. 4. This pulse delayer and modulator circuit corresponds to unit |0 of Fig. 1 and receives pulse input from the receiver unit over leads 28. Leads 28 may extend to the signal pulse synchronized pulse oscillator 22 of Fig. 2. Modulation frequency input for the pulse delayer modulator is impressed upon the circuit over leads I9 and transformer 45, the leads |9 extending to the balancing network unit I6 of Fig. 1. It should be noted that the condenser C' of the pulse oscillator modulator in the feedback circuit between the anode of tube 88 and the grid of tube 8| is adjustable, and that the resistor 6| in series between the grid of tube 8| and the transformer 45 is also adjustable. In order to get the maximum range of distance, the pulse delayer and modulator circuit of Fig. 5 is set so that the time delay units are arranged for minimum time delay for a particular pulse rate. This is done in Fig. 5 by adjusting the capacity of condenser C' to a minimum value and adiusting resistor 6| also to a minimum. However, in order to obtain minimum distances, the condenser C' is adjusted to give maximum capacity, and resistor 6| adjusted to give maximum resistance, thus giving maximum time delay. The pulse transmitter of Fig. 5, corresponding to unit |2 of Fig. 1, comprises a pulse magnetron 4| which is coupled to the pulse delayer and modulator circuit 80, 8| by way of a pulse keyer vacuum tube 43. The pulse keyer 43 is normally biased to be in an anode current cut-off condition, in which state there will be no potential drop across resistor 44. When the pulses over leads 28 flip or throw the circuit balance of the pulse delayer and modulator 88, 8| in one direction from the stable to the active state, the pulse keyer control electrode of tube 43 is pulsed negative with the only result that the already small or zero potential drop across resistance 44 in series with the anode to cathode of the keyer 43 remains zero, or is made momentarily slightly lower. However, when the circuit 88, 8| flops back again (i. e., restores itself), the control electrode of the keyer tube 43 is driven momentarily positive, resulting in a. large momentary potential across Ithe resistance 44 in series with the keyer tube. This large momentary potential across the resistance 44 occurs because of the fact that tube 43 passes current momentarily. This momentarily large increase in potential across the resistance 44 appears between the hot and cold-cathodes 82 and 83, respectively,`of the magnetron oscillator and causes this oscillator to produce a pulse of extremely high frequency oscillations. The magnetron is not claimed herein per se, and is of the controllable type described in my copending application Serial No. 470,768, filed December 31, 1942. This type of magnetron oscillator includes an anode having an even number of target portions which protrude inwardly toward the cathode and are symmetrically disposed around it. The hot cathode 82 serves to provide a priming current for building up a circulating space charge caused in large part by secondary emission from the cold cathode. A

magnetic field, which may be produced by a magnetizing coil which is here represented diagrammatically by the dot and dash line 84, produces fiux lines extending substantially parallel to the axes of the cathodes. Output energy from the anode is taken from a loop 85, as shown, and passed over a suitable transmission line 86 to the antenna by way of transmit-receive device 9, if such a device is employed. Although I have shown one particular type of magnetron oscillator as described in my copending application supra, it should be clearly understood that, if desired, other oscillators capable of producing extremely short pulses of ultra high frequency energy may be used inv place of the magnetron oscillator shown in the drawing. The ultra high frequency energy may correspond to a wavelength less than one meter. Also, the pulse output of tube 43 may control operation of a pulser capable of pulsing the whole anode power pulse input to the magnetron more or less according to common practice in present radar transmitters.

Fig. 6 shows an alternative form of adjustable pulse delayer and modulator and pulse oscillator circuit which can be used for the combined units I and l2 of Fig. 1. This particular circuit comprises a pulse input coupling tube 50, which receives positive input pulses from unit Il of Fig. 1 over leads 28 and passes these pulses on to adjustable pulse delayer and modulator vacuum tube circuit 5| by way of transformer 60. One winding of a pulse feed-back transformer 6| vis shown coupled to the pulse keyer having a tube 43, the latter controlling the high frequency pulse output energy from a suitable magnetron oscillator illustrated diagrammatically, by way of example only, by the reference numeral 9|. During most of the time, tube 50 is non-conductive and requires a positive pulse over leads 28 to make this tube carry current. Pulse keyer tube 43 is also normally non-conductive, in which condition there will be no potential difference across the resistor 44 in the anode circuit of the keyer tube. In the system of Fig. 6, the positive input pulses impressed upon leads 28 by the receiver unit |l, or from oscillator 22 of Fig, 2, cause pulses of anode current to pass through the pulse input coupling tube 50 which, by coupling over transformer 60, drives the diode anode positive in the pulse delayer and modulator tube 5|. As a result, the diode anode of tube 5| is made to carry rectified current to the cathode of the same tube. After the pulses, the grid or control electrode of tube 5| is left negative, thus blocking flow of main anode current for a time and causing the condenser 52 between the anode and cathode of the tube 5| to charge up to nearly full power supply potential through an adjustable charging resistance 55. After an adjustable time interval, the positive potential on the main anode becomes great enough and the negative grid potential of tube 5| leaks down to a value low enough to permit anode current to flow, which, by feed-back coupling through the transformer 60, results in a pulse of current very largely discharging the storage condenser 52. The resistance shown in the connection to the control electrode prevents substantial rectication of current due to positive feed-back potential and so leaves the grid almost without negative bias potential after the anode current pulse. Pulse potential from another winding on the transformer 6| (as shown) is applied to the pulse keyer 43 which causes a pulse of increased potential on the magnetron 9|, making it oscil- "At this time, it should be observed that when A 12 late momentarily and deliver a pulse of high frequency power to the output transmission line 85.

the pulse keyer tube 43 is normally cut-off between pulses applied thereto, the condenser 54 charges up over resistors 44 and 5B. When the tube 53 is pulsed positive by transformer 60, however, the tube 43 passes current and permits the condenser 54 to discharge across the magnetron 9| and the tube 43 in series. The adjustment of the time delay in the pulse delayer and modulator circuit is achieved by adjustment of the time constants of the resistance 81 and condenser 88 in the grid circuit of the tube 5|, and also by adjusting the time constants of the resistance 55 and condenser 52 in the anode circuit of the tube 5I. The modulation frequency input for modulating the time delay of pulsing of tube 5| is applied to the transformer 92 byway of leads I9 which, in turn, extend to unit I6 of Fig. 1. The oscillator 9| of Fig. 6 merely shows the essential elements of any well known magnetron,such as the magnetic field coil 84, the cylindrical anode 89 and the cathode 90. If desired, the circuit including the tube 4'3 and magnetron 9| of Fig. 6 can be substituted for the tube 43 and magnetron of Fig. 5. From the foregoing, it will be appreciated that by modulating the time delay at any one station, we automatically modulate or change the frequency of the pulses at both stations of the twoway communication system of the invention.

Although the invention has been described with particularity with regard to modulating the pulse rate or pulse frequency for conveying the intelligence, it should be understood that, if desired, the circuits can be so arranged that the extremely high frequency energy of the pulse can be modulated in accordance with the intelligence to be transmitted. Thus, for applying telegraph, telephone, facsimile or other types of modulation to the pulses, it is contemplated that any one of a considerable number of modulation schemes may be employed, including the following: (l) Wide band frequency or phase modulation to the radio carrier currents which are transmitted in the form of pulses and which can be received through integrating circuits at the receiver followed by frequency or phase modulation detectors which are unresponsive to amplitude modulation or which are preceded by amplitude limiters or their equivalent for removing amplitude modulation before detection. (2) Modulations of the frequency or phase of pulses transmitted from veach transmitter followed by reception with circuits responsive to variations in pulse frequency or timing. Circuits have already been described for this type of modulation. (3) Modulations of pulse amplitude followed by integration of pulse energy and amplitude modulation detection of the integrated energy. (4) Modulation in the length of pulses at each transmitter to vary the mean amplitude of currents arriving at each receiver in combination with amplitude modulation detection. In this case, it is assumed that the keying systems in each receiver for rendering the receiver responsive during only certain desired short time intervals are designed to result in responsive periods sufilciently long to include the longest required pulse while modulation is present. (5) Differential timing modulation of successive pulses transmitted in combination with receiver detectors responsive to this type of modulation following the teachings of my copending appliandere 13 cation Serial No. 367,688, led November 29, 1940. (6) Differential amplitude modulation of successive pulses in combination with detector systems responsive to this-type of modulation.

What is claimed is:

1. A pulse type communication system comprising a pair of stations separated by a wave transmitting medium, each station including apparatus for producing pulses which are short compared to the time intervals between them, and each station including a receiver for demodulating received pulses, means including a local oscillator associated with each receiver for controlling it to be responsive substantially solely at times registering with the repetition rate of the incoming pulses, an adjustable pulse delayer in circuit with the receiver of each station and receiving pulses therefrom, said delayer controlling the rate .of production of pulses in the transmitter of the same station, and means coupled to said adjustable pulse delayer for modulating the timing of the pulses passed thereby to said transmitter.

2. A pulse type communication system comprising a pair of separated radio stations, each station including apparatus for producing ultra high frequency pulses which are very short compared to the time intervals between them, and each station including a receiver for demodulating received pulses, a common directive antenna for the receiver and transmitter at each station, apparatus between said antenna and the elements of the station associated therewith for effectively uncoupling the receiver from the antenna when the transmitter is delivering power to the antenna, means associated with each receiver for controlling it to be responsive substantially solely at times registering with the repetition rate of the incoming pulses, an adjustable pulse delayer in circuit with the receiver of each station and receiving pulses therefrom, said delayer controlling the rate of production of pulses in the transmitter of the same station, and means coupled to said adjustable pulse delayer for modulating the timing of the pulses passed thereby to said transmitter.

3. A pulse type communication system comprising a pair of stations separated by a wave transmitting medium, each station including transmitter apparatus for producing pulses which are short compared to the time intervals between them, a receiver at each station for demodulating the received pulses, a directive antenna at each station in common to both the transmitter and receiver apparatus thereat, the directive antennas at both stations being so arranged as to be effective for communication therebetween, means associated with each receiver for controlling it to be responsive substantially solely at times registering with the repetition rate of the incoming pulses, an adjustable pulse delayer in circuit with the receiver of each station and receiving pulses therefrom, said delayer controlling the rate of production of pulses in the transmitter of the same station, and means coupled to said adjustable pulse delayer for modulating the timing of the pulses passed thereby to said transmitter.

4. A pulse type communication system comprising a pair of stations separated by a wave transmitting medium, each station including apparatus for producing pulses of high frequency energy which are short compared to the time intervals between them, and each station including a receiver for demodulating received pulses,

means associated with each receiver for controlling it to be responsive substantially solely at times registering with the repetition rate of the incoming pulses, said means including `a pulse oscillator whose natural frequency is near the repetition rate of the incoming pulses, and a vacuum tube circuit for synchronizing said pulse oscillator from the received pulses, said vacuum tubelcircuit having radio frequency selective circuits tuned to the frequency of the alternating current energy of said pulses, an adjustable pulse delayer in circuit with the receiver of each station-and receiving pulses therefrom, said delayer controlling the rate of production of pulses in the transmitter of the same station, and means coupled to said adjustable pulse delayer for modulating the timing of the pulses passed thereby to said transmitter.

5. A pulse type communication system comprising a pair of stations separated by a wave transmitting medium, each station including apparatus for producing pulses which are short compared to the time intervals between them, and each station including a receiver for demodulating received pulses, means including a local oscillator associated with each receiver for controlling it to be responsive substantially solely at times registering with the repetition rate of the incoming pulses, an adjustable vacuum tube pulse delayer in circuit with the receiver of each station and receiving pulses therefrom, said delayer being so constructed and arranged as to be responsive to pulses solely of a predetermined 'polarity above a certain value which are impressed thereon for controlling the rate of production of pulses in the transmitter of the same station, and means coupled to said adjustable pulse delayer for modulating the timing of the pulses passed thereby to said transmitter.

6. A distance selective pulse type communication system comprising a pair of separated radio stations, each station including transmitter apparatus for producing ultra high frequency pulses which are very short compared to the time intervals between them, and each station including a receiver for demodulating the received pulses, a common directive antenna for the receiver and transmitter at each station, means associated with each receiver for controlling it to be responsive substantially solely at times registering with the repetition rate of the incoming pulses, said means' including a pulse oscillator whose natural frequency is near the repetition rate of the incoming pulses, and a vacuum tube circuit for synchronizing said pulse oscillator from the received pulses, said vacuum tube circuit having radio frequency selective vcircuits tuned to the frequency of the alternating current energy of said pulses, an adjustable vacuum tube pulse delayer in circuit with the receiver of each station and receiving pulses therefrom, said delayer being so constructed and arranged as to be responsive to pulses solely of a predetermined polarity above a certain value which are impressed thereon for controlling the rate of production of pulses in the transmitter of the same station, and means coupled to l said adjustable pulse delayer for modulating the 15 intervals lying solely between periods of pulse transmission, means at said transmitter for modulating a characteristic of said `pulses in accordance with the intelligence tobe conveyed, and adjustable means in circuitwith said local oscillator for controlling the rate o'ffproduction of the pulses in said transmitter.

8. A distance selective wave system comprising a station having a transmitterv for sending short pulses of energy spaced in time an amount which is large compared to the time of each pulse, and a receiver at said station responsive for time intervals lying solely between ,periods of pulse transmission, means including an adjustable time delay circuit at said transmitter for modulating a characteristic of said pulses in accordance with the intelligence to be conveyed, said time delay circuit having adjustable impedances for varying the xed time delay. n

9. A distance selective Wave system comprising a station havinga transmitter for sending short pulses of energy spaced in time an amount which is large compared to the time of each pulse, and a receiver at said station responsive for time intervals lying solely between periods of pulse transmission, means including an adjustable vacuum tube pulse delayer circuit at said transmitter ior modulating a characteristic of said pulses in accordance with the intelligence to be conveyed, said vacuum tube pulse delayer having adjustable impedances for varying the xed time delay, and a vacuum tube keyer circuit coupling the output of said delayer and said transmitter,

l0. A distance selective wave system comprising a station having a transmitter for sending short pulses of energy having a wavelength less than one meter, a local oscillator controlling said transmitter through an adjustablev delay circuit, said pulses being of the order of one microsecond and less, and a receiver at said station having an output coupled to said local oscillator, means for suppressing said receiver during the time said transmitter is sending pulses, means for modulating the timing of said pulses in accordance with the signal to be transmitted, whereby pulses passed by said receiver to said local oscillator control the time and rate of production of the pulses to be sent out by said transmitter.

11. A distance selective wave system comprising a pair of stations each having a transmitter for sending short pulses of energy spaced in time an amount which is large compared to the time of each pulse, and a receiver at said station responsive for time intervals lying solely between periods of pulse transmission, means at said transmitter Afor modulating a characteristic of said pulses in accordance with the intelligence to be conveyed, and adjustablemeans for controlling the rate of production of the pulses in said transmitter in response to the output of said receiver, the receiver response periods of one station registering in time with the transmitter vsending periods of the other station. i

12. A distance selective pulse communication system comprising a station having a transmitter for sending short pulses of energy spaced in time an amount-which is large compared to the time of each pulse, and a receiver at said station for receiving pulsesfrom a remote station, said rev ceiver including a pulse oscillator and means for synchronizing said pulse oscillator in accordance with the received pulses',`a nd a circuit coupled to l said pulse oscillator f and `to said transmitter at the same station for controlling the time of transf 16 mission of the pulses from said transmitter to occur at intervals between received pulses.

13. A distance selective pulse communication system comprising a station having a transmitter for sending short pulses of energy spaced in time an amount which is large compared to the time of each pulse, and a receiver at said station for receiving pulses from a remote station, said receiver including a pulse oscillator and means for synchronizing said pulse oscillator in accordance with the received pulses, and a circuit coupled to said pulse oscillator and to said transmitter at the same station for controlling the time of transmission of the pulses from said transmitter to occur at intervals between received pulses, said circuit including a pulse delay circuit having adjustable impedances for controlling the phasing of the pulses passed thereby to said transmitter.

14. A distance selective pulse 'connnunication system comprising a station having a transmitter for sending short pulses of energy spaced in time an amountwhich is large compared to the time of each pulse, and a receiver at said station for receiving pulses from a remote station, said receiver including a pulse oscillator and means for synchronizing said pulse oscillator in accordance with the received pulses, and a circuit coupled to said pulse oscillator and to said transmitter at the same station for controlling the time of transmission of the pulses from said transmitter to occur at intervals between received pulses, said circuit including a vacuum tube pulse delay circuit having adjustable impedances for controlling within a range the amount of delay of the pulses passed thereby, to thereby control the transmtter, and modulating means coupled to said vacuum tube pulse delay circuit.

15. A distance selective pulse communication system comprising a station having a transmitter for sending short pulses of energy spaced in time an amount which is large compared to the time of each pulse, and a receiver at said station for receiving pulses from a remote station,v

said receiver including a pulse oscillator and means for synchronizing said pulse oscillator in laccordance with the received pulses, and a circuit coupled to said pulse oscillator and to said transmitter at the same station for controlling the time of transmission of the pulses from said transmitter to occur at intervals between received pulses, said circuit including a pulse delay circuit having adjustable impedances for controlling the phasing of the pulses passed thereby to said transmitter, and means for modulating the pulses at said transmitter.

16. A distance selective pulse communication system comprising a radio station having a transmitter for sending short pulses of energy spaced in time an amount which is large compared to the time of each pulse, and a receiver at said station for receiving pulses from a remote station, a common antenna for said transmitter and receiver, means connected between said antenna and said transmitter and receiver for eiectively uncoupling said receiver from said antenna when said transmitter is sending pulses, said receiver including a pulse oscillator and means for synchronizing said pulse oscillator in accold-V vtransmitter to occur at intervals between received pulses,

17 17. The method of communication between a first station and a second station which comprises radiating a carrier wave from said first station for discrete short periods separated by 18 rectification in said pulse oscillator and to reduce said cut-off bias to a value which allows said oscillator-detector to oscillate for a predetermined time interval when said pulse oscillator passes discrete, appreciably longer interval, receiving current, and a coupling vacuum tube between the said radiated carrier at said second station, radioutput of said oscillator-detector and the input of ating the carrier wave from said second station said pulse oscillator for affecting the timing of during a portion of the interval between said the pulses generated by said pulse oscillator. discrete periods, receiving said carrier wave from 22. A pulse System COmpriSIlg a signal input said second station at said rst station during circuit, a pulse oscillator-detector having a fresaid portion of the interval lbetween said discrete quency selective circuit, a. blocking oscillator, a periods when no carrier is radiated from said coupling tube between the output of said oscilrst station, controlling the operation of said lator-detector and the input of said blocking second station by successively delaying a controloscillator, a connection from said signal input ling impulse derived from the carrier radiated circuit to said frequency SeleClSiVe Circuit, 00nfrorn said first station, supplying an intermedinections from said frequency selective circuit and ate period of said delayed controlling impulse to from the input of said coupling tube to said blockcause radiation from said second station, utilizing oscillator so arranged as to normally bias ing the received carrier wave at said second stasaid oscillator-detector and said coupling tube t0 tion to limit reception from said first station to cut-off, said last connections supplying a positive periods when no carrier is radiated from said pulse to said oscillator-detector and coupling second station, and adjusting the amount of detube in response to the passage of current in said lay of said delayed controlling impulse to thereby blocking Oscillator, Said positive pulse being 0f select a narrow range of distances over which sufficient magnitude to cause said oscillator-decommunication between said stations is to be tector and said coupling tube to pass current. effective. 23. A pulse system comprising an oscillator- 18. Apulse repeater system comprising ablockdetector, a blocking oscillator, a coupling tube ing oscillator, a circuit for receiving pulses from between the output of said oscillator-detector and a remotely located pulsing station and for imthe input of said blocking oscillator, connections pressing the same on said blocking oscillator for from said blocking oscillator to the inputs of said synchronizing the same, and a pulse transmitter oscillator-detector and said coupling tube, said under control of said blocking oscillator. connections being so arranged as to normally bias 19. Apulse repeater system comprising a blocksaid oscillator detector and said coupling tube to ing oscillator, a circuit for receiving pulses from cut-off, said blocking oscillator delivering a pulse a remotely located pulsing station and for imto said connections whenever said blocking oscilpressing the same on said blocking oscillator for lator passes current, said pulse being of sufficient synchronizing the same, a pulse transmitter unmagnitude and sense to cause said oscillatorder control of said blocking oscillator, anda signal detector and coupling tube to pass Current m0- modulation circuit for modulating the pulses promentarily. duced by said transmitter. CLARENCE W. HANSELL.

20. A pulse system comprising a signal input circuit, an oscillator-detector having a frequency REFERENCES CITED Selctve ciruit; a continufmsly Operating pulse The following references are of record in the oscillator circuit, connections from both said fue of this patent: signal input circuit and said pulse oscillator to said frequency selective circuit, said connection UNITED STATES PATENTS from said pulse oscillator to said frequency selec- Number Name Date tive circuit being so arranged as to normally bias 2,323,944 Beatty Sept, 7, 1943 said oscillator-detector to cut-olf due to grid rec- 2,286,377 Roberts June 16, 1942 tication in said pulse oscillator and to reduce 1,523,374 Herten ,131120, 1925 said cut-olf bias to a value which allows said oscil- 1,742,902 Deloraine et a] Jam 7, 1930 latOr-detector to oscillate for a predetermined 2,110,543 Finch Mang, 1933 time interval when said pulse oscillator passes 1,923,093 Coyle Sept-26, 1933 Current 2,199,634 Koch May 7, 1940 21. A pulse system comprising a signal input 2,262,838 Deloraine et al Nov. 18, 1941 Circuit, an oscillator-detector having a frequency 2,266,401 Reeves Dee, 16, 1941 selective circuit, a continuously operating pulse 2,045,224 Gerhard June 23, 1936 Oscillator circuit, connections from both said 2,199,179 Koch Apr, 30, 1940 signal input circuit and said pulse oscillator to said frequency selective circuit, said connection FOREIGN PATENTS from said pulse oscillator to said frequency selec- Number Country Date tive circuit being so arranged as to normally bias 357,024 Great Britain Sept. 17, 1931 said oscillator-detector to cut-off due to grid Disclaimer 2,425,314.-Ularence W. Hansell, Rocky Point, N. Y. PULSE COMMUNICATION SYSTEM. Patent dated Aug.

12, 1947. Disclaimer filed Oct. l0, 1950, by

the assignee, Radio Corporation of America. Hereby enters this disclaimer to claims [Ofcial Gazette November 14,

18 and 19 of said patent. 

